A total hip prosthesis conventionally comprises, on the one hand, a femoral part constituted by a stem, at one end of which is fixed a femoral head defining a globally spherical convex articular surface and, on the other hand, a cotyloid part to be fixed to the bone of the pelvis, comprising for example a cotyloid metal cup in hemispherical form, inside which is housed an insert made of plastics material or ceramics in which the femoral head is articulated.
When such a total hip prosthesis is fitted, the surgeon implants, on the one hand, the femoral stem inside a cavity hollowed out longitudinally in the bone of the femur and, on the other hand, the cotyloid part of the prosthesis in a globally hemispherical cavity hollowed out in the bone of the pelvis. The direction of implantation of the femoral stem in the bone of the femur is globally imposed by the elongated shape of the femur bone, while the surgeon has greater liberty to choose the position of implantation of the cotyloid part in the cavity hollowed out in the pelvic bone. The choice of this position has a direct influence on the position of the axis of revolution of the theoretical cone of mobility of the implanted prosthesis, this axis of revolution corresponding in fact to the axis of revolution of the hemispherical cup connected to the pelvic bone.
It has been noted that the positioning of the acetabulum at the level of the zone of implantation of the pelvis has an effect on the mechanical behaviour of the implanted prosthesis. More precisely, when the prosthesis is articulated in movements of extreme amplitude, particularly in movements combining elementary displacements of the hip in flexion/extension, in abduction/adduction and/or in medial rotation/lateral rotation, it may happen that it is urged outside the cone of mobility of the prosthesis, in that case provoking a bearing contact between the femoral neck of the prosthesis and the edge of the acetabulum. Under these conditions, the prosthesis may be dislocated.
U.S. Pat. No. 6,205,411 proposes a method for fitting a hip prosthesis which assists the surgeon in implanting the prosthesis with a view to limiting the risks of subsequent dislocations of the prosthesis by adapting it to the anatomy of the patient treated. To that end, it is provided to use, on the one hand, a pre-operative simulator of the biomechanical kinematics of the patient's hip provided in virtual manner with the prosthesis to be subsequently implanted and, on the other hand, a device for per-operative guiding of the surgeon's gestures to fit the prosthesis, this device being controlled from the results issuing from the biomechanical simulation carried out by the simulator. To allow the simulator to determine an adequate positioning of the prosthesis to be implanted, it is necessary to provide it with a complete and detailed mapping of the patient's bone structure, particularly by means of non-invasive tomographic techniques. All these data are processed by computer in order to re-create the patient's osseous anatomy virtually, and then, still pre-operatively, to simulate its behaviour with a virtual prosthesis. This method therefore necessitates very considerable data processing means which are expensive, as well as a large amount of pre-operative data, which prolongs the duration and cost of hospitalization of the patient.
It is an object of the present invention to propose a surgical device which assists the surgeon more simply, more rapidly and more economically during the procedure of implanting a total hip prosthesis, with a view to limiting the risks of subsequent dislocations of the prosthesis, by being adapted as best possible to the anatomy of each patient treated.